Experimental and Theoretical Studies of the Richtmyer- Meshkov Instability with nonlinear Initial Stage at Low Mach Number.

Recent experiments of Zaytsev et al. (1991). and Dimonte et al. (1996) suggest that the large reduction of the perturbation growth rate relative to the Richtmyer impulsive model can be attributed to the high Mach number at which the experiment was performed. In the present work similar experiments were carried out in a shock tube apparatus at low Mach number. A shock wave, which travels from air to SF6 at a Mach number of 1.2, was the initiator of the instability. A single mode perturbation with relatively large ratio of amplitude to wavelength (a0 / λ ≈ 0.25 to 0.4) was imposed on the interface at t=0. Sets of experiments with negative and positive Atwood number were performed. A 2D simulation and a vortex model based on the model of Samatane and Zabusky (1995) were compared to the experimental results and good agreement was found. The growth rate, which was predicted by the simulation and supported by the model and the experiments, is lower by a factor of ~ 2.5 than that predicted by the Richtmyer impulsive model, in spite of the low Mach number. We conclude that the reduction of the growth rate for large initial amplitude depends more on the shock wave interface interaction than on the high Mach number effect (high compressibility effect).